Urban power supply systems are a part of a power supply system of the country and should be constructed technically rationally and economically soundly. The scheme of power supply of each separate city develops historically depending on local conditions. Change of a configuration of an existing network with the purpose of improvement of network parameters are connected with large capital investments. At construction of new transformer substations and new networks there is a necessity and an opportunity to carry out rational development of power supply system, as on a design stage so and constructions. For rational construction of power supply scheme the high profile has a correct choice of the location of substations for different level of voltage, zones and radiuses of service of consumers. In work the uniform and proved approach to the location of new substations and definition of service zones is offered. Modeling of service zone of substations is executed for the decision of this problem. Geometrical patterns by means of which it is possible rationally to cover territory of building of city are offered. The area of service zone of substation depends on its loading and density of loading. Actual densities of loadings at each level of a voltage are different and they form hierarchy of density of loading according to hierarchy of voltage. Graphic display of hierarchy of densities of loadings and theoretical definition of ratio between densities of loadings at different levels of a voltage is executed. The model of service zone of substations and pattern for accommodation of substations on territory of city in the form of a correct hexagon is chosen. Mathematical expressions for the basic sizes of patterns are received. Dependences of zones and radiuses of service depending on density of loadings for 110/10-20 кV and 10-20/0,4 кV two-transformer substations are constructed. The offered geometrical patterns can be used for the proved accommodation of substations on territory of city. As a result development of networks and urban power supply schemes will occur not chaotically and purposefully.